1. Field of the Invention
The present invention, in general relates to methods for placing instruments in bore holes and, more particularly, to methods for placing sensors and probes in direct contact with any of the surrounding strata of the bore hole.
There are potentially many reasons for placing sensors, probes, and various kinds of instrumentation in bore holes. Any geophysical property that one can wish to study is benefited by better placement techniques. Any subterranean measurement, such as temperature, movement of any kind, pressure, to name just a few are all candidates that benefit from improvements in the ability to place instruments.
One such area of investigation involves monitoring the flow characteristics of subterranean fluids. Monitoring the underground flow of water as well as chemical or radioactive contaminants is becoming increasingly more important. This information can be crucial to preventing the contamination of aquifers, and if it is reliable, it can be used to provide data that can in turn be used to plan and to augment mitigation techniques.
For example, the need for constructing underground barriers can be determined by having a sophisticated ability to measure minute underground fluid flow characteristics. If the flow of a contaminant can be detected and accurately mapped, then this data can be used in the formulation of abatement strategies.
For example, the type and size of an effective underground barrier that would be needed to contain the contaminants can be determined. Accurate monitoring is also useful in providing the ability to verify the efficacy of existing barriers and various other containment techniques. If, for example, the minute flow of contaminated fluids is better determined by improved sensor placement technologies, then the ability to monitor flows on both sides of an existing barrier will determine the efficacy of the barrier.
It is far better to know that an existing containment method, such as a barrier, has in fact failed than it is to falsely believe over time that it is working properly as potentially irreversible damage can then occur.
Prior techniques for placing instrumentation in bore holes have incurred many problems, some of which are so severe as to potentially invalidate the data that is acquired. The words "instrument" and "instrumentation", as used herein, are intended to refer to any piece of equipment that is to be placed underground and it includes all types of probes, sensors, transducers, and the like that can provide useful information of any kind.
As an example of problems encountered with prior art approaches, it is important to seal the entire bore hole after placement of instrumentation has occurred to prevent the accumulation of fluids in the hole. If fluid accumulates in the hole and surrounds the instrumentation (probes and sensors) the data they provide can be rendered suspect at best and in some cases even useless.
Prior art methods for placing instruments in a bore hole involve filling the bore hole with cement after the instruments have been placed. The technique for placing the instrumentation in the bore hole required attaching the instruments to an inflatable rubber bladder and lowering the bladder and instruments into the bore hole. The bag would then be inflated by pumping a gas through a tube into the bladder and then sealing off the tube at the surface. Cement would then be poured into the hole to fill it.
This approach has proven itself to not be reliable because the inflatable bladder can leak over time, thereby pulling the instruments away from a position of contact with the bore hole wall. If this occurs, all of the data that is collected is based upon factors that no longer exist (the assumption that the instruments are held in contact with the wall under pressure), and is therefore all invalid.
Furthermore, the cement does not provide a water-tight seal of the bore hole and fluids can accumulate in general proximity to the instruments and can even surround the instruments. If water accumulates proximate the instruments this thereby falsifies both the conditions as well as the data that is provided by the instruments.
Furthermore, fluids can migrate around the cement and pass through the bore hole in such fashion as to create new paths for their migration. In particular a fracture that is conducting a contaminated fluid near the top of the bore hole can convey the fluid through the bore hole to another separate fracture that is disposed lower in the bore hole. The contaminated fluid can continue to migrate as a result of the bore hole when it otherwise could not have done so because the cement does not provide a perfect seal of the interior of the bore hole. This is a potentially serious problem in that the bore hole (well) that is intended only to supply data can actually contribute to the problem of fluid migration.
The cement is also susceptible to erosion and deterioration. Acidic conditions, such as often occur with contaminated fluids and especially radioactive contaminants, can hasten the process. Therefore the prior art instrument placement techniques in bore holes has incurred many problems and a poor track record involving their long-term performance.
Also, the prior techniques do not provide any way to service or maintain the bore hole. Once the cement has been poured, there is no way to add extra cement, for example, somewhere along the length of the bore hole, should that become desirable. This might occur if erosion has removed some of the cement or if settling has occurred or if a traumatic event, such as an earthquake, has occurred.
Accordingly, there exists today a need for an improved method for placing instrumentation in a bore hole. Clearly, such a method would be useful and desirable.
2. Description of Prior Art
Methods for placing instrumentation in bore holes are, in general, known. The preceding discussions are believed to well describe the current known state of the art.
While the structural arrangements of the above described devices and methods may, at first appearance, have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices and methods.